Valves and valve assemblies are frequently employed in conjunction with the regulation of the flow of a fluid. Typical appliances are gas-fired installations, where the flow of a gas to a combustion chamber or to a burner is regulated. Examples of gas-fired installations include, but are not limited to, water heaters, boilers, stoves, dryers, deep fryers, fireplaces.
Valve assemblies typically provide one or several valve members. The valve members are arranged in a flow channel that connects the inlet of the valve assembly to its outlet. To open or close a gas valve, one or several actuators drive a valve member into or out of a flow channel.
Certain applications require modulating gas valves. Modulating gas valves allow precise control of the mass flow of a gas by adjustment of a valve member. As the position of the valve member of a modulated valve may be anywhere between fully open and fully closed, the flow of a gas may vary accordingly.
A gas valve assembly may actually provide several valve members that are sequentially arranged. With each valve member adapted to fully close the flow channel, a solution with two valve members achieves technical redundancy. That is, both of the valve members need to malfunction in order for the entire assembly to undergo failure.
Valve diagnosis may yield even more reliable solutions, especially in cases where a (catastrophic) failure of a gas valve is not acceptable. To that end, a gas valve may provide a plurality of sensors and a control unit to detect leakage and/or imminent failure.
The German patent DE102011000113B4 was granted on 14 Aug. 2013 and discloses a valve assembly 10 with two valve members 15, 16. The valve assembly according to DE102011000113B4 also provides a pressure sensor 18. The pressure sensor 18 is configured to measure gas pressure in a middle section 17 in between the valve members 15, 16. Diagnostic information about the valve can be derived from the measurement of pressure in the intermediate volume 17.
The pressure sensor 18 of the valve assembly of DE102011000113B4 connects to a controller 11. During a diagnostic check, the controller 11 opens or closes a first valve member 15 and then opens or closes a second valve member 16. In a subsequent check, the controller 11 reverses the sequence of opening or closing the valve members 15, 16. The controller will thus first open or close the second valve member 16 and then do the same with the first valve member 15. The reversal of the sequence aims at extending the useful life of the assembly 10.
The patent EP1236957B1 was granted on 2 Nov. 2006 and discloses a burner-operated device. The device comprises a valve 19 and a pressure sensor 28. Both the valve 19 and the pressure sensor 28 are connected to a control unit 30. The control unit 30 matches a flow of combustible gas to a flow of air for optimum performance of the burner-operated device.
The patent EP1236957B1 teaches the pressure sensor 28 may in an alternate embodiment also be a mass flow sensor. In contrast to a pressure sensor 28, a mass flow sensor will allow for a direct determination of gas flow.
The aforementioned publications EP1236957B1 and DE102011000113B4 do not focus on harnessing a flow sensor to perform valve diagnosis. Instead, they deal either with long service life or with optimum gas to air ratio. In particular, EP1236957B1 and DE102011000113B4 do not teach how to come up with diagnostic equipment that responds to rapid changes in flow rate. Also, the disclosures of EP1236957B1 and of DE102011000113B4 do not focus on equipment that is capable of measuring gas flow in service and of performing valve diagnosis. That is, the combination of accurate flow measurements and of reliable diagnosis has not been dealt with in detail.
Start-up operations of the burner that are unnecessary to the unavailability of combustible gas are to be avoided. The gas input pressure is typically checked by a gas pressure sensor or by a gas pressure switch before a fire control unit runs the start-up sequence. In particular, a check of gas input pressure is performed before opening both gas valves.
In addition, the input gas pressure is checked by a pressure sensor to avoid excessive input pressure. A condition with excessive input pressure may, for instance, occur due to a failed pressure governor.